Mulberry is known as ‘the best health fruit in the 21st century’， however it is not resistant to storage and is extremely perishable. In the research and development of new probiotic fermented mulberry juice functional products， there is a lack of special strains. The black pearl mulberries are used as raw materials， and 12 new probiotic lactic acid bacteria isolated and identified from natural fermented foods are used as test strains. By comparing the acid production characteristics and growth ability of the test strains in the preliminary mulberry juice medium， the test strains were preliminarily screened； the sensory quality of the optimized mulberry juice culture medium was evaluated by the preliminary screening strain， and the strains were re-screened； the quality of the pure-bred fermented mulberry juice products of the re-screened strains was analyzed and evaluated. We studied the laxative effect of pure-bred fermented mulberry juice products on test mice. The results showed that: after preliminary screening and re-screening， a new probiotic suitable for fermenting mulberry juice， namely Lactobacillus plantarum P17， was obtained； the pure-bred fermented mulberry juice product of P17 strain was uniform and stable in tissue. Rich fruity aroma and fermented aroma， physical， chemical and nutrient composition comply with relevant national and industry standards， and the content of live probiotic bacteria reaches 8.7×108 CFU/mL and is rich in polyphenols (199.59 g/kg ± 0.12 g/kg) and anthocyanins (29.12 mg/L ± 0.06 mg/L). Its shelf life is 25 days in 4 ℃， and the number of viable probiotic bacteria is still 9.5×107 CFU/mL； P17 pure-bred fermented mulberry juice product shortened defecation time， promoted small intestinal movement and content discharge in constipation model mice and improves the constipation of mice.